It is known to prepare compositions comprising polyphenylene ethers and poly(vinyl aromatic) compounds, e.g., polystyrene. These are useful per se as molding resins, see, e.g., Cizek, U.S. Pat. No. 3,383,435. In Sumitomo, German Pat. No. 1,939,033, pre-isolated polyphenylene ether, styrene and xylene are suspended in water and the styrene is polymerized using a free-radical initiator. In Bennett, Copper and Katchman, U.S. Pat. No. 4,152,369, polyphenylene ether is prepared in styrene using a copper-amine catalyst or a lead oxide catalyst, then the styrene is polymerized by bulk or emulsion techniques. Typically long reaction times are required. In Yamanouchi et al., U.S. Pat. No. 3,700,750, the suggestion is made to graft polyphenylene ether onto crystal homopolystyrene. In applicant's earlier issued U.S. Pat. No. 3,956,242 (and related patents), it is suggested to employ a manganese chelate catalyst for the oxidative coupling of a phenolic compound to a polyphenylene ether in a basic reaction medium. The polymer is then removed from solution by adding an antisolvent. The foregoing patents are all incorporated herein by reference.
The practical combination of a polyphenylene ether and a poly(vinyl aromatic) compound by the foregoing process has until now been stymied by slow vinyl aromatic conversions and the resultant low molecular weight of the polymers obtained from using the polyphenylene ether reaction mixtures directly, because of the by-product contaminants present. In spite of this, it is obviously desirable to use as the reactant for vinyl aromatic polymerization, an unisolated product of a polyphenylene ether polymerization. This is because anti-solvent isolation of polyphenylene ether from a conventional polymerization and solution in vinyl aromatic, e.g., styrene, is economically unattractive. Moreover, with copper-amine catalysts, in order to remove and recycle the amine portion of the catalyst, an acid extraction is traditional. It has now been found that a manganese chelate catalyst can be substituted and left in the polymer reaction solution and a selective liquid-liquid extraction of base included as a separate step. The extraction removes base-reactive by-products and low molecular weight polymers, nonpolymerizable monomer impurities, and colored species, all of which are left behind in conventional acetic acid extraction. The consequence of such base-reactive, non-acid-extractable residues being left in the polyphenylene ether solution is to interfere with subsequent polymerization of the vinyl aromatic, lowering its molecular weight and conversion rate.
The catalyst used in the present process is the manganese chelate system described in the above-mentioned U.S. Pat. No. 3,956,242. The system is capable of giving low by-product quantities of diphenoquinones (DQ when starting with 2,6-xylenol). Furthermore, when styrene is substituted for the more conventional toluene as a polymerization solvent, this catalyst system appears to generate even less base-reactive by-products. Because the preferred manganese (benzoin oxime).sub.2 system is very efficient and operates at low manganese levels, catalyst entrainment is possible without adverse effect on the final product. Indeed, it is a most unexpected advantage of the present process to be able to leave the polyphenylene oxide polymerization catalyst in the polyphenylene oxide-vinyl aromatic composition, and that such action does not seriously harm the product performance characteristics.